All these regions are extremely dry, and most are extremely hot too, as you can see, these regions include the Sahara, the Gobi desert, Arizona, Nevada, Central Australia, Iran and large chunks of the Middle East. Whether an area is classified as arid or not depends on the evapotranspiration that I mentioned last time, which is the sum of evaporation and transpiration from plants. This image illustrates evapotranspiration:

Evapotranspiration. Image from Wikipedia

All the arid, and semi arid regions have more evapotranspiration than precipitation (fancy word for rain and snow etc, stuff that falls out of the sky). This means these areas are not able to support much plant life, and consequently, the number of animals which can live in the region are limited. There are of course, plants which survive, and indeed thrive in these conditions, and they have some amazing adaptations to allow them to do so, the same for the animals which live in these conditions.

It is often assumed that deserts have no rain at all, but, some have over 25cm a year. The evapotranspiration however, is greater than this.

So, what makes these regions so dry, and mostly hot?

You remember last time I mentioned the ITCZ? Well, arid climates fall around 30°S and 30°N, which is between the first green lines above and below the equator in this image:

Arid regions are located around the bands with an H to the north and south of the Equator (marked by the ITCZ on this image). Image from Wikipedia

As I mentioned in my first post on climate (HERE), the air circulations from the equator to the edge of the tropics are known as Hadley cells. To recap, the warm air rises at the equator, and moves north or south (depending on the hemisphere), as it cools, it begins to descend. This descent occurs around 30°S and 30°N. This air has deposited much of the moisture it picked up at the equator already (mostly over the rainforest regions), so it is much drier when it reaches these latitudes.

For interested geeky parties like me, these latitudes are also known as the Horse Latitudes (Allegedly due to some old naval tradition for running around on a deck of a ship with a horse…). They are characterised by high pressure, which leads to clear, cloudless skies (due to the lack of water vapour in the atmosphere) and very high temperatures. Up here in the North, when we have high pressure it is associated with those lovely (Or not, depending on your perspective) hot summer days, and those crispy cold awesome winter days (Guess which I prefer!). The lack of clouds in these regions means that whilst the days can be scorchingly hot, the nights can be extremely chilly. The highest recorded temperatures are from desert regions, and they can reach over 40°C in summer on a regular basis.

The deserts which are not hot all year round tend to be the ones at a higher altitude, and these occasionally receive snow in the winter, but their summers are still very hot, and they have very little rainfall.

The semi-arid regions are found bordering desert regions, and the main difference between these, and the arid regions is that they receive a little more rainfall, and so are able to maintain a wider variety of plants and animals.

Now, I should mention that whilst these areas are deserts, Antarctica is also one huge desert, but is not on the list of arid regions. This is because Antarctica has a polar climate, which we will get to in a later post..

Next time, we will move onto the climate I am most familiar with, the wet, windy temperate climates, where we will bump into the Jet Stream, the Gulf Stream, and probably a few other streams too! I will try not to make it too long, promise!

So, as promised last post, today we will look at the different climate zones on the planet, and some of the main features of each.

As mentioned last post, climate refers to the long term patterns in a region, and these are usually classified using the Köppen classification system, which divides the Earth into regions with similar annual variations in climate. This is how the planet looks under this system:

Köppen climate classification map. Image from Wikipedia

Don’t be put off by all the strange abbreviations at the bottom, the basic thing is that there are 5 main groups, and then lots of sub-groups within each one.

Starting at the beginning of the alphabet:

Group A is the Tropical climate regions, this is broadly the band around the equator, where we find tropical rain forests (group Af), monsoons (Am), and Savannah regions (Aw).

These regions have some of the most productive places on the planet, covering the Amazon Rainforest, the Indonesian rainforests, and the rainforests of central Africa. They also encompass the great plains of Africa, the Serengeti, and places in the US such as Hawaii (Aw) and Florida (Am) and the northern coast of Australia (Aw).

So, what does it mean to have a tropical climate? Well, it means the mean (average) temperature is 18 degrees centigrade (Which is a nice warm day for me here in Denmark!), it also means that the day length is roughly equal throughout the year, and the temperature does not have the wide range of seasonal, or daily variations you find in the mid-latitudes.

Looking a little deeper into each: Af, the Rainforest zones, are the zones closest to the equator, these have minor variations in weather throughout the year, being situated in the Intertropical Convergence Zone that we covered last post. This image shows the location of the ITCZ in January, and July each year, and you can see that it lines up with the rainforest, and other tropical zones.

Intertropical Convergence Zone location. Image from wikipedia

The rainforest zones have a lot of rain, each month, the average rainfall is around 60mm, which means they get 720mm of rain, on average, every year. The actual rainforests themselves have far more than this, with an average 200cm of rain per year.The reason for this difference is that not all locations within the rainforest zone are actually rainforests, there are cities, and arable lands, and grassland within these areas.

These regions, as well as being very warm, are very humid (As warm air can contain more water than cold air, and there is less wind than in other regions to disperse the moisture heavy air). Much of this humidity is from evaporation from the oceans, but large rainforests such as the Amazon have high levels of evapotranspiration (Evaporation from plants, and transpiration, which is the loss of water from plants when they have their stomata open) that much of the rain which falls over these rainforests actually comes from within it, meaning that they have their own mini water-cycle going on! This is also why rainforests have a higher rainfall than the zone as a whole.

The tropical monsoon zones (Am) are characterized by, as the name implies, a monsoon, and have a dry month, and little annual variation in temperature.

We usually associate the term monsoon with extremely heavy downpours, but, the term monsoon does not refer to the rain specifically, but to the change in wind direction, which brings this rain. The change in wind direction has different causes on different continents, but, is (usually) predictable, and arrives at the same time every year, meaning many of these regions have agriculture which relies on the arrival of the monsoon each year at a certain time for the crops, and any delay or shift in timing can have a large impact on the crops, and the food supply.

The monsoon we are most familiar with is the Indian monsoon, so I will briefly explain the mechanism behind this.

In India, in the summer, the air is very warm, the further you go into the continent, the warmer the air becomes, and at the northwest end of the sub-continent is a desert, the Thar desert, which has extremely warm air during the summer months.

This warm air rises, and because the air which has risen needs to be replaced, cooler air moves in, and this air moves from the ocean northwards over the continent. This air contains a lot of moisture, from evaporation over the ocean.

So, now we have this very wet air moving in to replace warm air which has risen, which would result in normal summer rains if it was not for the rather large blockade at the northern end of India, which we know as the Himalayas. The warm, moisture filled air cannot move further north into Asia due to the mountains, and it is forced to rise. As it rises, it cools, and cool air cannot hold as much water as warm air, so, like the bottom of a water balloon bursting, the moisture is deposited out of the atmosphere back to the ground.

Whilst this is vital for agriculture and the plants on the subcontinent, there is also a lot of damage caused every year by flooding and landslides, with houses and roads washed away.

Chittagong in Bangladesh is a city within the tropical monsoon zone, and these next images show the average temperature, and the rainfall for each month. Note the low variation in maximum temperature, and the very obvious spike in rainfall during the monsoon season.

The cool thing for me about the Indian monsoon is that it only exists because of the Himalaya mountain range blocking the passage of the air further into Asia. Why do I think this is super cool? Because, the Himalayas are a relatively new mountain range, geologically speaking, and are only there because India went zooming across the ocean faster than continents usually move (one theory suggests this is due to the plate being thinner than most other continental plates, and so lighter, and able to move faster. It may also have got a slight speed boost by passing over a hotspot in the Earths mantle) and smacked into Eurasia around 50 million years ago. To put this in a time perspective, this was after the era of the dinosaurs. The Himalayas are currently growing at around a centimeter every year, due to the Indian plate moving north-east faster than the Eurasian plate is moving north.

Finally, onto the Savannah zones (Aw). These regions have very obvious wet and dry seasons. While these areas can have a lot of rain during their wet months, it is not enough rain to qualify them as monsoons. This change in weather is due to the movement of the ICTZ, and the rainbelts which lie around it.

This image illustrates the dry season in Brasilia, which is as marked a difference as the monsoon in India:

So…it has been a while. You know how it goes, you get caught up in something (in my case my final semester of my bachelor) and next thing you know, it is 8 months later, and then you feel awkward about returning after such a long break.

Anyway, I was asked if I would write up some posts on the IPCC report, so I thought it was as good a reason as any to get back into blogging!

I thought I should start out with an introduction to climate, as for me, the systems themselves are fascinating, and for a lot of people, climate is some abstract concept only heard in relation to carbon dioxide and climate change, when in reality, it is so much more. I hope I can show you at least a little window into our awesome planet in this post.

Climate is defined as “The pattern of variation in temperature, wind, humidity, atmospheric pressure and other variables over a long period in a given region”

This is different from weather, which is the temperature, wind, humidity, atmospheric pressure etc at a given time in a specific location.

So, climate is “It is cold in Sweden”, weather is “It snowed today in Stockholm”.

The main factor affecting climate on Earth is the incoming solar radiation, which is unequally distributed across the surface of the Earth, being more concentrated at the equator, and more diffuse at the poles.

This means the atmosphere is heated more at the equator, and less at the poles. As hot air rises, and cold air sinks, this unequal heating causes movement of air. The air heated at the equator rises and moves towards the poles, whilst the cooler air moves towards the equator to replace the rising air.

This results in loops of air circulation, which are known as Hadley cells in the tropical regions (near the equator), Ferrel cells in the mid latitudes, and polar cells at the poles.

Global Atmospheric Circulation Cells. Image from wikipedia

In the areas where the air in the Hadley cells is descending, we find desert regions, this is due to the air being cooler, and containing less water than the warm, rising air at the equator.

These cells of circulating air play an important role in many of the large scale phenomena such as the monsoon circulation in Asia, formation of hurricanes, and the jet streams and trade winds, which are caused by a combination of the circulating air cells, and the rotation of the Earth.

The rotation of the earth means that air currents do not move in a straight line, but appear to rotate to the left, or right, depending on the hemisphere. These two videos demonstrate the effect. This first one is a simple experiment showing the phenomena:

This second video shows this effect in action, and is an animation of annual air circulation (I actually had an image of this as my desktop background for quite some time, as I really love the visualization). You can see the deflection of the air currents, and the band across the equatorial areas known as the Intertropical Convergence Zone (ITCZ), which is where the northern and southern hemisphere air meets.

Next post in this series will cover the major climate zones on the planet, and some of the driving forces and phenomena in each of them.

Exams all done now, so back to the fun of blogging about awesome animals!

So far, the molluscs we have looked at have had some sort of shell, but not all molluscs have taken the shelled path.

Today, and in the next post, we are going to meet some which prefer to be without shells, and are, in my opinion, some of the most beautiful molluscs around: So, without further ado, let me introduce you to todays topic: the nudibranch (from the Latin nudus meaning naked, and the Greek brankhia meaning gills, so literally, “naked gills”)

Berghia coerulescens, a species of nudibranch. Image from wikipedia

This group of animals has a whole lot of awesomeness going on, some of which we will cover today, and then it will spill over into the next post too!

For today, lets take a look at the one in the video, it is called Glaucus atlanticusm and the reason it is awesome for me, is that, despite being a squishy little sea-slug like thing, around 3cm long, it eats these:

Physalia physalis (Better known as the Portuguese Man O’ War) Image from wikipedia

Now, if there is one thing we know about Portuguese Man O’ War, it is that it has a very nasty sting, due to the trailing tentacles being full of cells which can fire toxic darts into its prey (or into an unsuspecting persons leg) (See link HERE for post about Man O’ War)

So how does Glaucus cope with these stings? There is a hypothesis that it releases mucus while eating the tentacles (Yes, because it is small, and the PMOW is much larger, it nibbles its way up the tentacles), which protects its insides from the stings, which can remain active for a period of time after the Man O’ War is dead.

To make it even cooler, it takes some of these stings, and uses them in its own defense. It goes a little something like this:

Glaucus eats the tentacle with the stinging nematocysts within it. Some of these pass through digestion, and end up in growths on the outside of the animal, called cerata. These then become part of the animals defense systems, meaning it can fire them at any attackers.

It has primitive teeth (denticles) which it uses to chomp through its prey, but also to hang onto them

So, this is a fairly cool animal so far, but, it gets even more amazing when you find out some other details about it.

This lovely little animal floats upside down, so its top side is in the water, and its underside is at the surface. It floats because it has a bubble of air in its stomach, but this means it has no way of steering, so it floats around as the winds or currents take it

In common with many fish which are found near the surface (Sharks for example), it uses a form of camouflage which is known as countershading

Its “top” (Which is in the water) is light silvery grey, so it is difficult to spot from below, whilst its “bottom” is a deeper blue, or blue and white, which helps it blend in with the water when seen from above.

I will leave this last image of Glaucus atlanticus for you, and next post we will look at some of the other animals in this family.

So, its the new year now, I hope everyone had a nice new year, with not too many hangovers!

Last time, way back in October, I wrote about bivalves (HERE), and wanted to pick up where we left off, so today is about their vision and movement, as promised.

I am going to focus on scallops (Pectinidae) as they have both interesting eyes, and strange movement.

Let’s start out with the eyes. You and me have two eyes, and this is a fairly common number of eyes to have, Scallops however, seem to be quite fond of eyes, usually having between 40 and 70, but they can have up to 100!

Eyes on a giant scallop, the dark blue dots along the rim of the shell. (Image from Wikipedia)

Now, not all eyes function the same way as ours do, we have already met organisms with eyespots, which are just a bunch of light sensitive cells able to distinguish between light and shade so the organism can move away from predators, or towards the light for photosynthesis. (HERE)

The eyes of scallops are what is known as concave mirror eyes. These are “simple” eyes, which have a reflective layer at the back of the eye, which bounces light back onto the cells which are able to process the light. As they have so many eyes, positioned along the edge of their shell, they are able to follow an object as it moves past them, rather than having to move their eye to keep it in focus. They also have two retina in each eye, one which responds to light, and one which responds to darkness.

Scallop Eye, showing the reflecting surface at the back which bounces light to the rods. (Image from rewiring-neuroscience.com)

I have been trying to find other diagrams showing this, and have come up with a couple of sites, depending on how techy of an explanation you want:

Opthobook.com has a very simple diagram (HERE), and a little video explaining the basics of eye variation (HERE). For the more technical diagrams and explanations, this paper by M.F.Land (1965) is interesting (HERE), as well as this illustrative paper by Colicchia et al (2009) (HERE). One final paper on comparative morphology (similarities and differences between the parts in different organisms) from Speiser & Johnson (2008) (HERE)

So, apart from having more eyes than that teacher at school who always spotted you chatting (Not that I was ever talking during class, of course!), what else is cool about these bivalves?

Well..I think sometimes a video says way more than I can by rambling, so lets take a look at how these scallops move:

This movement is done by using muscles at the back of the shell to open and close it, this pushes water out of the shell, and the scallop shoots off like one of those bottle rockets you make as a kid with fizzy drinks! They can control the direction of the jet of water, so it is not a completely random motion.

So, after an extended break, normal service is resuming, although the post today will be slightly off the usual topic of the evolutionary journey.

As I mentioned yesterday, I have been writing my bachelor project, and I thought I would share with you a little of the topic I have written it on.

I could write a post which would keep my good e-friend Argyle Sock very happy, with lots of statistical stuff in it, but, honestly, if I see the terms “not normally distributed” one more time, my head may go pop!

Also, the actual topic is much cooler than the stats (even though they are very cool too of course!).

I would like to introduce to a group of pigments called anthocyanins. These are the reason for the colour of blueberries, blackberries, some grape species, olives and many other fruits, and purple or red colourings in flowers, like these pansies:

Violet pansies: The purple colour is caused by anthocyanins in the petals. Image from Wikipedia

The amazing bright red colours you see in autumn leaves is also down to anthocyanins.

So..why have I spent this last semester writing about pretty red colours?

Well..here is where it gets a little more interesting (not that pretty purple flowers are not interesting of course!)

Anthocyanins are also found in leaves which are not about to fall off the tree. Some plants have red leaves when they are young, and some plants can turn on and off the red colouring under certain conditions

Sciencey term for the day: This is called phenotypic plasticity….a phenotype is the appearance something has due to certain genes being expressed. If a phenotype is plastic, it means it can change under certain environmental conditions.

So, I have been looking at a particular plant, which is usually green and grows in shallow lakes. These lakes dry out a bit in the summer (Yes, we have summer in Denmark, sometimes!), and so some of these plants may end up out of the water. If this happens, 90% of these plants turn red, until the water covers them again.

The reason I have been looking at this plant (with a bunch of other people who are much better at scary maths than me!) is because it is not entirely clear exactly what the red stuff in the leaves does. In some plants it seems to act a bit like a sunscreen, in others it seems to stop the plant being eaten by insects.

The amazingly awesome Leaf-cutter ants (Several posts on them will come along a bit later in our evolution journey) will not harvest leaves which are red. This may be because insects do not see red the way we do, they do not have the parts in their eyes which can collect red light.

Leaf Cutter Ants carrying leaves off to their underground farm Image from wikipedia

It has also been suggested that anthocyanins can help plants survive during cold or drought conditions, so, there seems to be a whole lot of stuff that this pigment helps with.

The health food industry has even been getting in on it, and you can buy anthocyanin supplements…this is because in plants, they work as anti-oxidants, and we are always hearing about how having free radicals is bad for us, and so we should eat blueberries, or whatever the cool food to eat this week is (its usually the most expensive one!). I am not entirely sold on this idea, as, last time I checked, I am not a plant.

So anyway, I have been working with an awesome group of my fellow students, and we have been trying to make these poor plants very stressed to see what happens. We grew them under some very bright lights, and then did some tests where we zapped them with..well…an even brighter light, to see what they did.

Personally, I find the plant we have been studying more interesting than the actual pigment we have been looking at, although, that has been fascinating to learn about. The plant itself has no stomata, which are the holes which plants use for taking in carbon dioxide and giving out oxygen and look like this in extreme close-up:

Stomata on a tomato leaf Image from wikipedia

Because this plant has no stomata, it has to breathe through its roots, which is extremely cool! This means that it can only live in lakes which do not have a lot of nutrients in them, because, if you increase the amount of nutrients which end up at the bottom of a lake, you decrease the amount of carbon dioxide which is produced by the bacteria eating all the dead stuff at the bottom.

As more dead stuff ends up at the bottom of the lake, the bacteria down there start using up more oxygen than is available, and so the only ones that can live there produce methane (CH4) instead of carbon dioxide (CO2). This is what is found in my favourite land-types, the wetlands, bogs and moors.

Oh, yes, I forgot to show you a picture of the plant! This is the little thing I have spent 6 weeks growing, and then several weeks cutting up and zapping with bright lights!

Lobelia Dortmanna. Image from wikimedia

So, I hope I did not bore you too much with the slightly off-topic post, and next time we will pick up on the evolutionary trail again, with some weird and wonderful creatures. If you prefer plants, hang in there, we will get to them in a few million years or so!